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212 guitar closed back cab build
212 guitar closed back cab build
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Old 21st December 2009, 10:37 PM   #1
Yanoplathizo is offline Yanoplathizo  United Kingdom
diyAudio Member
Join Date: Dec 2009
Default 212 guitar closed back cab build

I stuck this in another forum before but having seen the other cab buildthreads - the links for which i set upon at hte bottom of this page I was forced to reconsider my placing. I also considered the instrument thread but, having seen the sucsess of such threads here decided against it. Sorry for any clutter!

Hello guys! Nice forum BTW! First thread!

I am going to build a 212 guitar cab to go under my amp for now and be used in the future with some tube head kits ect.

I have the specs on the speakers that I want to use - celestion gk12k-100s

G12K-100 8ohm
d - 0.26m Sd is equivalent area created by d.
Re - 7ohm
Fs - 85Hz
Qms - 10.25
Qts - 0.53
Qes - 0.56
Mmt - 29g
Cms - 0.13mm/N
Vas - 51litres
Bl - 13.6Tm
Rms - 1.45kg/s
Xmax - 1mm
Pe - 100W

I have some small woodworking experience but no speaker system design experience. However, despite the info on celestions website about disregarding the thiele principle I would like to aim for the best to allow for any mistakes!

I have used a number of programs to work out my dimensions and have been rewarded with different numbers - I plan to use 18mm Baltic birch ply for both the baffle and the walls.

Here are my internal dimensions:

Set 1-
Height = 35.0cm cm
Width = 56.6 cm
Depth = 21.6 cm

got from here:Enclosure Calculator -Closed Back - 2 speakers

And the other set - i used bass box 6 for these


Can anyone tell me yay or nay for either of these sets of values? Then i can hit the local DIY for some wood!

Cheers and thanks!

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Old 21st December 2009, 11:57 PM   #2
PeteMcK is offline PeteMcK
diyAudio Member
Join Date: Feb 2002
Location: Western Sydney
'I stuck this in another forum ' & you still got the wrong one, a mod will move it sooner or later...
as suggested in the other thread, copy a Marshall cab, guitar speakers are not the same as Hi Fi speakers, and using programs to calculate dimensions is almost pointless...
(& dimensions are useless if they have no units...)
Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 22nd December 2009, 12:56 AM   #3
ChrisA is offline ChrisA  United States
diyAudio Member
Join Date: Jan 2008
The web site is right, you don't get better results using TS parameters. The reason is that the low E on a standard tune guitar is about 80Hz if you play an open e-string. Every other note is higher. There simply is no deep bass. Guitars are midrange instruments. If you were building a bass cab it would be different. Four string basses go to 40Hz, five strings are lower to the 30's

The way to build them is to figure the largest size cab you can stand. Then think hard if you can use ertical placement. one above the other. This is best, if you can because the sound is spread wider but not taller

I built using pine boards 12" wide for the sides and top then 3/4" hardwood ply for the baffle. I made the backs in three parts one is glued in place but two can be removed if I want to convert to open back. On one "slat" i put 3" ports.

So now I have the option of closed back with 3" round ports or a full 4" wide slat open across the back or remove two slats for a 60% open back. I get the best bass with the ports.

Don't let the hifi people tell you that pine cabs will resonate, that is a "Good Thing" in a musical instrument.

I used finger joints but you can use 3/4" battons in all inside corners but in with wood glue and large screws romthe outside. counter sink the screws and fill with Bondo

Last edited by ChrisA; 22nd December 2009 at 12:59 AM.
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